Among people over the age of 65 years, fall-related injuries are the leading cause of death from injury. Forty percent of hospital admissions among people over the age of 65 years are reported to be the result of fall-related injuries, resulting in an average length of stay of 11.6 days. Each year, an estimated one third of older adults fall, and the likelihood of falling increases substantially with advancing age. The average medical cost of a fall is more than $20,000, and the total cost of falls is expected to reach $32.4 billion in 2020.
In 2005, a total of 15,802 persons over 65 years died as a result of injuries from falls. However, the number of older adults who fall and who sustain only minor or moderate injuries and seek treatment in clinics or physician offices is unknown. To estimate the percentage of older adults who fell during the preceding 3 months, the CDC has analyzed data from the 2006 Behavioral Risk Factor Surveillance System (BRFSS) survey. The results of that analysis indicated that approximately 5.8 million persons aged 65 years or older, or 15.9% of all U.S. adults in that age group, fell at least once during the preceding 3 months, and 1.8 million (31.3%) of those who fell sustained an injury that resulted in a doctor visit or restricted activity for at least 1 day. The percentages of women and men who fell during the preceding 3 months were similar (16.4% versus 15.2%, respectively), but women reported significantly more fall-related injuries than men (35.7% versus 24.6%, respectively).
Procedural prevention programs attempting to reduce the incidence of falls have to-date had mixed effectiveness, in part because the preventive measures address only a subset of the antecedent factors that lead to falls and in part because they place almost all of the burden of falls-prevention upon personnel other than the person who is at risk of falling and making the faller a passive non-participant. In that connection, a motivation for some embodiments of the invention is that, were non-demented people whose near-term risks of falling are elevated or increasing notified of that risk, many of those fallers would respond to such notifications by proactively self-initiating preventive measures, including temporarily refraining from transfers or other risky movements and contacting caregivers for help. Psychologically, this is far preferable to patient passivity and reactive responses by caregivers, insofar as persons at risk of falling not only fear falls; they also fear loss of independence and freedom. They do not like being disenfranchised in decisions about their own care, and they do not adhere to prevention programs that “medicalize” their situation and displace control to other authorities, including caregivers.
Falling is associated with common chronic diseases, such as Alzheimer's or other forms of dementia; peripheral neuropathies associated with diabetes or other conditions; Parkinson's disease; tremor; extrapyramidal dyskinesias that may be associated with psychiatric medications; cerebrovascular accident or transient ischemic attacks; cardiac problems including cardiac arrhythmias; diminished visual acuity; muscle weakness; lower-extremity joint replacements; and other conditions. However, while the absence of such conditions does reduce fall risk to a degree, it does not exclude the possibility of falling. It is for this reason that so much effort has been expended over the past 30 years on developing predictive models, such as the Berg Balance Scale, the Timed [Get]-Up-and-Go Test, and other metrics.
Mechanisms and types of falling have been the subject of several studies. Slips account for a high percentage of falls and subsequent injuries in community-dwelling older adults but not in young adults. This phenomenon suggests that although active and healthy older adults preserve a mobility level comparable to that of young adults, these older adults may have difficulty generating efficient reactive postural responses when they slip. This study tested the hypothesis that active and healthy older adults use a less effective reactive balance strategy than young adults when experiencing an unexpected forward slip occurring at heel strike during walking. This less effective balance strategy would be manifested by slower and smaller postural responses, altered temporal and spatial organization of the postural responses, and greater upper trunk instability after the slip. Kinematic data were collected from the right (perturbed) side of the body. Although the predominant postural muscles and the activation sequence of these muscles were similar between the two age groups, the postural responses of older adults were of longer onset latencies, smaller magnitudes, and longer burst durations compared to young adults. Older adults also showed a longer coactivation duration for the ankle, knee, and trunk agonist/antagonist pairs on the perturbed side and for the knee agonist/antagonist pair on the nonperturbed side. Behaviorally, older adults became less stable after the slips. This was manifested by a higher incidence of being tripped (21 trials in older vs. 5 trials in young adults) and a greater trunk hyperextension with respect to young adults. Large arm elevation was frequently used by older adults to assist in maintaining trunk stability. In an attempt to quickly reestablish the base of support after the slips, older adults had an earlier contralateral foot strike and shortened stride length. Thus the combination of slower onset and smaller magnitude of postural responses to slips in older adults may result in an inefficient balance strategy. Older adults needed secondary compensatory adjustments, including alengthened response duration and the use of the arms, to fully regain balance and prevent a fall. The shorter stride length and earlier contralateral foot strike following the slip indicate use of a more conservative balance strategy in older adults.
Typical stability assessments characterize performance in standing balance despite the fact that most falls occur during dynamic activities such as walking. The objective of one study was to identify dynamic stability differences between fall-prone elderly individuals, healthy age-matched adults, and young adults. Three-dimensional video-motion analysis kinematic data were recorded for 35 contiguous steps while subjects walked on a treadmill at three speeds. From this data, we estimated the vector from the center-of-mass to the center of pressure at each foot-strike. Dynamic stability of walking was computed by methods of Poincare analyses of these vectors. Results revealed that the fall-prone group demonstrated poorer dynamic stability than the healthy elderly and young adult groups. Stability was not influenced by walking velocity, indicating that group differences in walking speed could not fully explain the differences in stability. This pilot study supports the need for future investigations using larger population samples to study fall-prone individuals using nonlinear dynamic analyses of movement kinematics.
Maintaining balance and postural stability while performing functional activities is critical to an individual's independence and quality of life. When individuals are unable to maintain their total-body center of mass (COM) within the base of support, a loss of balance may result, leading to a fall. Effective interaction between the environment and the neuromuscular and musculoskeletal systems allows an individual to generate the ground reaction forces relative to the COM necessary for maintaining and recovering balance during expected and unexpected situations. The swing and support legs have a role in regulating angular impulse during fall recovery and the balance recovery strategies used by younger adults and older adult nonfallers and fallers is different. The multijoint dynamics and neuromuscular control used during fall recovery at the total-body, joint, and muscle levels are relevant aspects that are considered. Understanding the fall recovery mechanisms successfully used by younger and older adults allows us to begin to identify effective intervention strategies that target specific populations.
It is because of these factors that an improved predictive-preventive method and system would be valuable, and in embodiments of such methods and systems, prediction classification or decision-support alert signals emitted by the system are provided at logistically convenient times far enough in advance of a fall's occurrence to allow for effective preventive intervention in a majority of cases. Moreover, embodiments of such a method and system should be inexpensive and suitable for a much larger population who are at moderate risk of falls. Such a system would find use as a tool not only for surveillance and triaging the general medical-surgical patients in hospitals and other acute-care venues but also for ambulatory, free-living individuals such as athletes and the general elderly population who have one or more risk-factors for falls.
Effective fall preventive interventions vary, and optimal selection and personalized tailoring of them will depend upon the patient's context, gender, age, medications, neurological conditions such as Parkinsonism, history of previous falls, and other factors. In the case of a previously asymptomatic ambulatory person, effective preventive interventions may include consultation with the personal physician or nurse or physiotherapist, or presentation at a nearby outpatient department for diagnostic assessment and monitoring. In the case of a person with existing, known neurological conditions, effective preventive interventions may include admission to hospital for observation and neurological exams, provision of visiting nurse services, placement in an assisted-living or other long-term care facility, consideration for adjustment of medication regimen, or other alternatives.
Conventional pressure- and proximity- and accelerometry-based monitoring apparatus has been shown to have inadequate statistical sensitivity and specificity for the purpose of predicting falls.
When measurements rely upon motion patterns as the trigger or sentinel event for predicting incipient falling, the predictions are generally only relevant when the person is ambulating. Additionally, the advance notice provided by disturbed respiratory pattern signals is so short (milliseconds to seconds) as to preclude effective interventions to prevent the predicted falling occurrences. For example, the Bed-Ex™ Patient Occupancy Monitoring System and Motion Knowledge System's FallSaver™ and other ‘proximity mat’ and ‘pressure mat’ monitors for bed or chair surfaces have been used to detect and remotely signal unattended patient ambulation or [attempted] transfer-in-progress, and thereby predict patient falls. However, these often do not give a warning or alarm far enough in advance to enable nurses or other caregivers to reach the patient in time to assist them and prevent the fall.
Many prior art methods involve cumbersome, complex, expensive and/or invasive instrumentation, or require a skilled operator in attendance.
The most accurate predictive methods, such as multi-axis accelerometry, are expensive, are not widely available, are only performable by subspecialty-trained providers, and are only applicable to a small subset of patients who are already known to be at risk of falling based on other attributes.
The methods involve expensive measurements, such as genomic or proteomic laboratory tests that are not widely available and that have a performance turnaround time of many hours or days before the results and prediction are available for use, such that the prediction or classification is not timely with respect to interventions aimed at preventing the predicted occurrences.
The methods are sensitive to, and may be compromised or entirely confounded by, individual variations in patient anatomy and activities, such as transfers from chairs or wheelchairs or beds, transfers with slide-boards or grab-bars other prosthetics, patient movement and positioning, diurnal variations, etc.
The methods are sensitive to, and may be compromised or entirely confounded by, individual variations in operator positioning of proximity or pressure or accelerometer sensors on the patient's body or variations in the timing and method of acquiring the specimens or data that will enter into the prediction and classification.
A major deficiency of prior art is false-negative error rate and the absence of immunity to differences in daily activities and behavior mix. A further deficiency is activity-specificity, for example, the ability to detect or predict forward-falling while walking but not backward-falling and not falling while climbing stairs or running. Stride length decreases with advancing age, and a further deficiency of prior art is a restricted range of applicability in terms of gait and stride length.
Still a further deficiency is that existing systems do not take into account diurnal variations in persons' capabilities. For example, Parkinsonian patients tend to have greater stability deficits early and late in the day, and lesser deficits in the middle of the day. Whereas, some embodiments of the invention are sensitive to time-varying patterns in fall-risk.
Still a further deficiency is that some existing systems make or rely on assumptions about the cognitive status of the subject, this despite the fact that dementia and other cognitive and psychological factors clearly affect the precautions or lack thereof that are taken by fallers.
Still a further deficiency is that existing systems are unable to account for orthostatic hypotension, visual acuity, medication use, basic or instrumental activities of daily living, and other factors.
Still a further deficiency is that existing systems do not account for rotational acceleration, this despite the fact that various recovery movements that interrupt falls involve rotation of the torso and despite the fact that some types of falling involve rotations. Accelerometers are primarily able to measure 3-axis 3-degree-of-freedom acceleration in 3-D Cartesian coordinates. And, while it is theoretically possible to impute rotations (pitch, roll, yaw) from 2 or more 3-axis accelerometers, the angular precision and accuracy of doing so is presently inferior to the precision and accuracy of measuring rotations with a digital gyroscope.
Still a further deficiency of existing systems is that calibration and periodic recalibration of accelerometer output in V/m/sec2 in all three dimensions (which may be expensive and time-consuming) are required for accuracy. In contrast, some embodiments of methods and systems of the invention produce accurate predictions that are insensitive to accelerometer offset and drift; that require only infrequent checks to be sure that all three axes of acceleration detection are still functional; that permit the outputs in the measured 3 axes to diverge considerably from each other in gain or scale so long as each one is itself maintains approximately linear response; and that use ‘relative’ instead of ‘absolute’ acceleration readings, and thereby offer a distinct advantage in terms of ease-of-use and long-term cost-of-ownership.
Still further, no mathematical or biomechanical models have to-date appeared that are able to predict falling from a wheelchair or other prosthetic devices that are prevalent in rehabilitation or long-term care venues.
Moreover, an important consideration for widespread acceptability of a system and method for fall prediction and prevention is that the apparatus not unduly stigmatize the subject. The elderly staunchly protect their independence and resist most measures taken to protect them that might have a second-effect or indirect consequence of alerting their caregivers to diminished capability, causing the caregivers to reactively restrict the person's autonomy.
The necessity of moving an elderly person to a nursing home often is revealed by evidence denoting the risks attendant to allowing the person to remain at home. The fear of being placed in a nursing home is sufficiently strong for many that they will aggressively hide evidence or obfuscate occurrences of falling that may lead caregivers or authorities to take the decision to place them in a nursing home.
However, an apparatus that reinforces the autonomy of the wearer—enabling the wearer to accurately recognize and predict risks or trends in risks and self-initiate appropriate mitigations, refraining from motions or types of activity while the elevated risk is present, thereby preventing occurrences of falling—would be welcomed. The adverse outcomes would be prevented, and the wearer would remain independent and in control of their activities for a longer period of time than typically would otherwise happen. They would not be distressed in connection with autonomy-preserving cover-ups and obfuscation.
None of the prior art has examined mathematical stability properties of the measured variables, however; nor has the prior art made use of continuous realtime measurements over long periods of many hours. Despite the existence of pressure and proximity and accelerometer monitor type recording equipment for approximately 20 years, the analysis of long-timeseries data is traditionally restricted to abnormal patterns denoting falls' occurrence, and calculation and study of antecedent timeseries patterns, and other parameters are never performed. Only small selected portions of the recorded data are subjected to detailed analysis, and the rest are discarded unexamined or ignored.